a) Field of the Invention
This invention relates to test charts for metamorphopsia, which permit detection of metamorphopsia and quantitative evaluation of metamorphopsia.
b) Description of the Related Art
Ophthalmologic diseases, especially age-related macular degeneration (ARMD), central serous chorioretinopathy, macular pucker, macular hole and the like, all of which feature development of a lesion at the macula, often result in cases in which patients sense by themselves an eye problem called xe2x80x9cmetamorphopsiaxe2x80x9d that an object is seen as distorted in shape due to a disorder in the arrangement of photoreceptor cells on the retina. This metamorphopsia develops a symptom, which is specific to macular diseases as opposed to symptoms detectable by other subjective tests on vision, visual field and the like. Finding of this specific symptom is, therefore, extremely important in early diagnosis of metamorphopsia and also in checking in the course of the same disease.
For the diagnosis of metamorphopsia, a test chart called xe2x80x9cAmsler gridxe2x80x9d has been used for many years. This Amsler grid can determine existence of metamorphopsia, but can by no means perform any quantitative evaluation of metamorphopsia. To the best knowledge of the present inventor, no test charts have heretofore been available for permitting quantitative evaluation of metamorphopsia.
An object of the present invention is, therefore, to provide test charts for metamorphopsia, which can determine existence of metamorphopsia and can quantitatively evaluate a degree of metamorphopsia with extreme ease in a short time.
To allow a patient himself or herself to notice distortion in visual images caused by metamorphopsia, stimulation to the retinal surface by a continuous straight line of a predetermined length is needed. Through a clinical study on patients suffering from metamorphopsia, the present inventor found that the distortion in visual image caused by metamorphopsia gradually becomes unnoticeable to patients themselves as this line is changed from a dotted line of a smallest inter-dot interval toward a dotted line of a largest inter-dot interval via dotted lines of gradually-varying, intermediate inter-dot intervals between the smallest inter-dot interval and the largest inter-dot interval. The present inventor also found that use of this tendency makes it possible to quantitate a degree of metamorphopsia with extreme ease in a short time. These findings have now led to the completion of the present invention.
In one aspect of the present invention, there is thus provided test charts for metamorphopsia, which comprises a plurality of dotted lines of predetermined lengths. These dotted lines consist of a dotted line having a smallest constant inter-dot interval, a dotted line having a largest constant inter-dot interval, and remaining dotted lines having constant inter-dot intervals, respectively, which fall within an intermediate interval range between the smallest constant inter-dot interval and the largest constant inter-dot interval.
The test charts for metamorphopsia according to the present invention can determine existence of metamorphopsia and also can quantitatively evaluate a degree of metamorphopsia with extreme ease in a short time.